Drilling and Completion Fluids and Their Applications

Abstract

This invention relates to the field of oil extraction and discloses a drilling and completion fluid and its application. The drilling and completion fluid comprises the following components in parts by weight: 1.5-2 parts of a filtration reducer, 0.3-0.5 parts of a viscosity modifier, 0.5-1.5 parts of an inhibitor, 1.5-2 parts of a lubricant, 0.5-1.5 parts of a water-locking agent, 5.5-8.8 parts of a plugging agent, and 100 parts of water. The drilling and completion fluid provided by this invention exhibits high temporary plugging rate, high mud cake acid dissolution rate, and high post-acid washing flowback rate, effectively protecting the microfractured reservoir of tight gas reservoirs, stabilizing the wellbore, facilitating the release of natural production capacity, and increasing production.

Description

Technical Field

[0001] This invention relates to the field of oil extraction, specifically to a drilling and completion fluid and its application in the protection of microfractured reservoirs in tight gas reservoirs. Background Technology

[0002] In recent years, with the continuous improvement of oil and gas exploration and development, the development of tight sandstone oil and gas resources has gradually increased, and China's tight sandstone oil and gas has achieved commercial-scale exploitation.

[0003] Tight sandstone gas reservoirs have poor physical properties and very low matrix permeability, making them discontinuous, low-porosity, and low-permeability natural gas reservoirs. Furthermore, the reservoir's natural structure is riddled with microfractures, and the main damaging factors are water lock-in and water sensitivity, as well as reservoir contamination caused by the intrusion of drilling and completion fluid filtrate and solid particles, resulting in irreversible damage to the reservoir. In addition, tight gas reservoirs have low single-well production. To improve single-well productivity, directional or horizontal wells are often drilled to increase the reservoir's venting area. This leads to a larger and longer contact area between the drilling and completion fluids and the reservoir, resulting in greater reservoir damage. Inadequate protection of these natural gas reservoirs will affect well production; therefore, drilling and completion fluids must have good protective effects and low damage to the gas reservoir.

[0004] Existing drilling and completion fluids are often formulated with pre-hydrated clay slurry, which contains a large number of fine solid particles, has a high filtration loss and high surface tension, and a large amount of free water invades the sandstone reservoir, which can easily cause water phase damage to the gas reservoir. Moreover, it has a weak ability to seal micro fractures in natural structures, and the large intrusion of drilling and completion fluid filtrate and solid particles can easily cause reservoir contamination. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of existing drilling and completion fluids causing water phase damage in tight sandstone reservoirs, weak sealing ability of natural structural microfractures, and easy reservoir contamination. This invention provides a drilling and completion fluid and its application in the protection of microfractured tight gas reservoirs. This drilling and completion fluid is a low-density, clay-free fluid that can efficiently seal natural microfractures, reduce filtration loss, avoid or reduce solid-liquid phase blockage and water-locking damage to tight gas reservoirs during construction, improve single-well natural productivity, and allow acid treatment to dissolve blockages in the sealed layer, effectively protecting the reservoir.

[0006] To achieve the above objectives, the first aspect of the present invention provides a drilling and completion fluid comprising the following components in parts by weight: 1.5-2 parts of a filtration loss reducer, 0.3-0.5 parts of a viscosity modifier, 0.5-1.5 parts of an inhibitor, 1.5-2 parts of a lubricant, 0.5-1.5 parts of a waterproofing agent, 5.5-8.8 parts of a plugging agent, and 100 parts of water.

[0007] A second aspect of the present invention provides an application of the drilling and completion fluid provided by the present invention in the protection of microfractured reservoirs in tight gas reservoirs.

[0008] The beneficial effects that can be obtained by the present invention through the above technical solution include:

[0009] The drilling and completion fluid provided by this invention features low density and no clay. While ensuring wellbore stability, it reduces the fluid density to mitigate overpressure water lock. It can be used as a protective fluid for tight gas reservoirs as well as a drilling fluid, exhibiting excellent viscosity and shear stress properties to meet on-site construction requirements. The filtration reducer, viscosifier, and plugging agent work synergistically to quickly and efficiently seal natural microfractures, achieving a plugging rate greater than 90%, preventing leakage and reducing filtration loss, improving pressure resistance, and achieving a core permeability recovery rate of over 90%. This reduces reservoir damage, effectively protects the reservoir, facilitates the release of natural production capacity, and increases production. The average acid solubility of the mud cake is greater than 80%, allowing it to be quickly dissolved and dispersed by acid during completion operations, facilitating its complete removal from the wellbore and flushing to the bottom, thus clearing the gas flow channels from the reservoir to the wellbore. Detailed Implementation

[0010] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0011] The first aspect of the present invention provides a drilling and completion fluid comprising the following components in parts by weight: 1.5-2 parts of a filtration reducer, 0.3-0.5 parts of a viscosity modifier, 0.5-1.5 parts of an inhibitor, 1.5-2 parts of a lubricant, 0.5-1.5 parts of a waterproofing agent, 5.5-8.8 parts of a plugging agent, and 100 parts of water.

[0012] Under this weight ratio, the components work together to have a good synergistic effect. For example, in addition to playing their main functional roles, the filter loss reducer, thickener, and blockage agent also have a synergistic effect.

[0013] The present invention does not limit the selection of the filtration loss reducing agent. Preferably, the filtration loss reducing agent is selected from at least one of carboxymethyl cellulose, modified starch, humic acid, resin-based filtration loss reducing agents, and acrylamide polymers.

[0014] According to a specific embodiment of the present invention, preferably, the filtration loss reducing agent is selected from carboxymethyl cellulose and / or modified starch;

[0015] Preferably, the viscosity of the carboxymethyl cellulose is 100-300 mPa·s.

[0016] The present invention does not limit the selection of modified starch. Pregelatinized starch obtained by acid hydrolysis or alkaline hydrolysis can be used; etherified starch, such as carboxymethyl starch, hydroxypropyl starch, etc., can be used; and graft copolymerized starch, such as graft copolymerized starch initiated by cerium salt initiator, potassium permanganate initiator, manganese pyrophosphate initiator, etc., can be used.

[0017] According to a specific embodiment of the present invention, carboxymethyl starch is preferred, but not limited to carboxymethyl starch. Both carboxymethyl starch and carboxymethyl cellulose can be obtained by purchase, and the present invention will not elaborate further on this.

[0018] The present invention does not limit the choice of thickener, but preferably it is selected from at least one of xanthan gum, modified guar gum, modified cellulose and acrylamide polymers.

[0019] According to a specific embodiment of the present invention, preferably, the tackifier is xanthan gum, which can be obtained by purchase, and the present invention will not elaborate further on this.

[0020] The present invention does not limit the selection of inhibitors, but preferably, they are selected from at least one of polyamines, pitch, polyols, silicates and ionic inorganic salts.

[0021] According to a specific embodiment of the present invention, preferably, the inhibitor is a polyamine, more preferably an oligomeric polyamine (total amine value ≥ 2.0 mmol / g, weight-average molecular weight ≤ 10000 g / mol). The polyamine inhibitor can be prepared in-house or purchased. The polyamine inhibitor of the present invention was purchased from Renqiu Chengfa Petroleum Technology Co., Ltd., brand number CFY-01 (total amine value 4.5 mmol / g).

[0022] The present invention does not limit the choice of lubricant. Preferably, the lubricant is selected from at least one of diesel-based lubricants, mineral oil-based lubricants, vegetable oil-based lubricants, sulfonated tall oil lubricants, polymeric alcohols and synthetic esters.

[0023] Polyols have good lubricity, are environmentally friendly, easy to maintain, and inexpensive. According to a specific embodiment of the present invention, the lubricant is preferably polyethylene glycol and / or polyglycerol.

[0024] More preferably, the lubricant is polyethylene glycol, the average molecular weight of which is 300 g / mol. Polyethylene glycol can be obtained by purchase, and this will not be described in detail here.

[0025] The present invention does not limit the selection of waterproofing agents. Preferably, the waterproofing agent is selected from at least one of low-carbon monohydric alcohols, alcohol ethers, nonionic surfactants and fluorocarbon surfactants.

[0026] According to a specific embodiment of the present invention, the waterproofing agent of the present invention was purchased from Shida Innovation Co., Ltd. in Dongying City, Shandong Province, and its brand name is SDFS-1.

[0027] According to the present invention, preferably, the sealing agent is selected from at least one of nanopolymers, calcium carbonate, highly acid-soluble fibers, and ultra-low permeability treatment agents.

[0028] According to a specific embodiment of the present invention, preferably, the sealing agent is a nanopolymer, calcium carbonate, highly acid-soluble fiber, and an ultra-low permeability treatment agent, wherein the weight ratio of the nanopolymer, calcium carbonate, highly acid-soluble fiber, and ultra-low permeability treatment agent is (1-2):(2-3):(1.5-2):(1-1.5). Within this range, the nanopolymer, calcium carbonate, highly acid-soluble fiber, and ultra-low permeability treatment agent can play a good synergistic role.

[0029] This invention does not limit the selection of nanopolymers; preferably, the nanopolymer has a median particle size D. 50 The nano-polyester exhibits high size matching with microcracks below 0.9 μm. The nano-polyester of this invention was purchased from Shandong Deshunyuan Petroleum Technology Co., Ltd., brand name NP-1.

[0030] The present invention does not limit the selection of calcium carbonate. Preferably, the calcium carbonate is selected from ultrafine calcium carbonate with an average particle size of 1250-2500 mesh.

[0031] The present invention does not limit the selection of highly acid-soluble fibers. Preferably, the length of the highly acid-soluble fibers is 20-50 μm and the diameter is 0.5-3 μm. The highly acid-soluble fibers of the present invention are purchased from Shida Innovation Co., Ltd. in Dongying City, Shandong Province, with the brand name SDCF-1 (length 3-12 μm and diameter 1-2 μm).

[0032] The present invention does not restrict the selection of ultra-low permeability treatment agent. Preferably, the particle size of the ultra-low permeability treatment agent is 50-1500 mesh. The ultra-low permeability treatment agent of the present invention was purchased from Dongying Shida Innovation Co., Ltd., and the brand name is SDN-1.

[0033] According to the present invention, preferably, the drilling and completion fluid further comprises 0.1-0.2 parts by weight of a pH adjuster to adjust the pH of the drilling and completion fluid to 8-11;

[0034] Preferably, the pH adjuster is caustic soda, which makes the drilling fluid present an alkaline environment, effectively improving the efficiency of other treatment agents, etc.

[0035] According to the present invention, preferably, the density of the drilling and completion fluid is 1.02-1.08 g / cm³. 3 .

[0036] According to the present invention, preferably, the apparent viscosity of the drilling and completion fluid is 22.5-28.5 mPa·s, and the plastic viscosity is 16-20.5 mPa·s.

[0037] According to the present invention, preferably, the dynamic shear force of the drilling and completion fluid is 6.5-8 Pa, and the static shear force is (2-2.5) / (4.5-6) ​​Pa / Pa.

[0038] A second aspect of the present invention provides an application of the drilling and completion fluid provided by the present invention in the protection of microfractured reservoirs in tight gas reservoirs.

[0039] Example 1

[0040] The drilling and completion fluid provided in this embodiment for the protection of microfractured reservoirs in tight gas reservoirs consists of the following components in parts by weight: 0.2 parts caustic soda, 2 parts filtration loss reducer (carboxymethyl cellulose), 0.5 parts thickener (xanthan gum), 1.0 part inhibitor (polyamine CFY-01), 1.5 parts lubricant (polyethylene glycol, average molecular weight 300 g / mol), 1.0 part waterproofing lockant SDFS-1, 1.5 parts plugging agent (nanopolyester NP-1, 3 parts micron-sized ultrafine calcium carbonate, 1.5 parts high acid-soluble fiber SDCF-1, 1 part ultra-low permeability treatment agent SDN-1), and 100 parts water.

[0041] Example 2

[0042] The drilling and completion fluid provided in this embodiment for the protection of microfractured reservoirs in tight gas reservoirs consists of the following components in parts by weight: 0.2 parts caustic soda, 1.5 parts filtration loss reducer (carboxymethyl cellulose), 0.3 parts thickener (xanthan gum), 1.2 parts inhibitor (polyamine CFY-01), 2 parts lubricant (polyethylene glycol, average molecular weight 300 g / mol), 1.5 parts waterproofing lockant SDFS-1, 2 parts plugging agent (nanopolyester NP-1, 2.0 parts micron-sized ultrafine calcium carbonate, 2.0 parts high acid-soluble fiber SDCF-1, 1.5 parts ultra-low permeability treatment agent SDN-1), and 100 parts water.

[0043] Example 3

[0044] The drilling and completion fluid provided in this embodiment for the protection of microfractured reservoirs in tight gas reservoirs consists of the following components in parts by weight: 0.2 parts caustic soda, 2.0 parts filtration loss reducer (0.5 parts carboxymethyl cellulose, 1.5 parts carboxymethyl starch), 0.5 parts thickener (xanthan gum), 1.5 parts inhibitor (polyamine CFY-01), 2 parts lubricant (polyethylene glycol, average molecular weight 300 g / mol), 1.5 parts waterproofing lockant SDFS-1, 1.5 parts plugging agent (nanopolyester NP-1, 2.5 parts micron-sized ultrafine calcium carbonate, 1.5 parts high acid-soluble fiber SDCF-1, 1.5 parts ultra-low permeability treatment agent SDN-1), and 100 parts water.

[0045] Example 4

[0046] The method of Example 1 is the same, except that the weight proportions of nano-polyester, calcium carbonate, highly acid-soluble fiber, and ultra-low permeability treatment agent are different. The specific implementation method is as follows:

[0047] The drilling and completion fluid consists of the following components in parts by weight: 0.2 parts caustic soda, 2 parts filtration loss reducer (carboxymethyl cellulose), 0.5 parts thickener (xanthan gum), 1.0 part inhibitor (polyamine CFY-01), 1.5 parts lubricant (polyethylene glycol, average molecular weight 300 g / mol), 1.0 part waterproofing lockant SDFS-1, 3 parts plugging agent (nanopolyester NP-1, 1.5 parts micron-sized ultrafine calcium carbonate, 1 part high acid-soluble fiber SDCF-1, 1.5 parts ultra-low permeability treatment agent SDN-1), and 100 parts water.

[0048] Example 5

[0049] The method is the same as in Example 1, except that the composition of the sealing agent is different. The specific implementation method is as follows:

[0050] The drilling and completion fluid consists of the following components in parts by weight: 0.2 parts caustic soda, 2 parts filtration loss reducer (carboxymethyl cellulose), 0.5 parts viscosifier (xanthan gum), 1.0 part inhibitor (polyamine CFY-01), 1.5 parts lubricant (polyethylene glycol, average molecular weight 300 g / mol), 1.0 part waterproofing lockant SDFS-1, 3 parts plugging agent (nanopolyester NP-1, 3 parts micron-sized ultrafine calcium carbonate, 1 part ultra-low permeability treatment agent SDN-1), and 100 parts water.

[0051] Example 6

[0052] The method of Example 1 is followed, except that the composition of the sealing agent is different, and the nano-polyester is replaced with petroleum resin. The specific implementation method is as follows:

[0053] The drilling and completion fluid consists of the following components in parts by weight: 0.2 parts caustic soda, 2 parts filtration loss reducer (carboxymethyl cellulose), 0.5 parts viscosifier (xanthan gum), 1.0 part inhibitor (polyamine CFY-01), 1.5 parts lubricant (polyethylene glycol, average molecular weight 300 g / mol), 1.0 part waterproofing lockant SDFS-1, 1.5 parts plugging agent (petroleum resin, 3 parts micron-sized ultrafine calcium carbonate, 1.5 parts high acid-soluble fiber SDCF-1, 1 part ultra-low permeability treatment agent SDN-1), and 100 parts water.

[0054] Comparative Example 1

[0055] The method is the same as in Example 1, except that the weight percentages of the drilling and completion fluid components are different. The specific implementation method is as follows:

[0056] The drilling and completion fluid consists of the following components in parts by weight: 0.2 parts caustic soda, 0.5 parts filtration loss reducer (carboxymethyl cellulose), 0.2 parts thickener (xanthan gum), 0.5 parts inhibitor (polyamine CFY-01), 0.5 parts lubricant (polyethylene glycol, average molecular weight 300 g / mol), 0.5 parts waterproofing lockant SDFS-1, 1.0 part plugging agent (nanopolyester NP-1, 1 part micron-sized ultrafine calcium carbonate, 1.0 part high acid-soluble fiber SDCF-1, 0.5 parts ultra-low permeability treatment agent SDN-1), and 100 parts water.

[0057] Comparative Example 2

[0058] The method of Example 1 is the same, except that the weight proportions of the filtration loss reducer, thickener, and blocker are different. The specific implementation method is as follows:

[0059] The drilling and completion fluid consists of the following components in parts by weight: 0.2 parts caustic soda, 0.5 parts filtration loss reducer (carboxymethyl cellulose), 1.5 parts thickener (xanthan gum), 1.0 part inhibitor (polyamine CFY-01), 1.5 parts lubricant (polyethylene glycol, average molecular weight 300 g / mol), 1.0 part waterproofing agent SDFS-1, 0.9 parts plugging agent (nanopolyester NP-1, 1.8 parts micron-sized ultrafine calcium carbonate, 0.9 parts high acid-soluble fiber SDCF-1, 0.6 parts ultra-low permeability treatment agent SDN-1), and 100 parts water.

[0060] Test Example 1: Drilling and Completion Fluid Performance Test

[0061] Test method: GB / T 16783.1-2014 Field testing of drilling fluids for the oil and gas industry - Part 1: Water-based drilling fluids

[0062] The results of drilling and completion fluid performance tests are shown in Table 1 below:

[0063] Table 1

[0064]

[0065]

[0066] As shown in Table 1, the drilling and completion fluids in each embodiment have moderate viscosity and shear stress, low API fluid loss and high-temperature, high-pressure fluid loss, effectively preventing drilling fluid filtrate from entering the reservoir, high rolling recovery rate, and good performance, meeting the requirements of on-site construction. Compared to Example 1, Examples 4-6 show reduced viscosity and shear stress, increased fluid loss, and a slightly lower rolling recovery rate. Compared to Example 1, Comparative Example 1 has different weight proportions of drilling and completion fluid components; the drilling and completion fluid in Comparative Example 1 shows reduced viscosity and shear stress, increased fluid loss, and a significantly lower rolling recovery rate. Compared to Example 1, Comparative Example 2 has different weight proportions of filtrate reducer, viscosifier, and plugging agent; the drilling and completion fluid in Comparative Example 2 shows reduced viscosity and shear stress, increased fluid loss, and a significantly lower rolling recovery rate.

[0067] Test Example 2: Testing the protective performance of drilling and completion fluid on microfractured rock reservoirs.

[0068] Test methods: Refer to SY / T 6540-2002 "Indoor Evaluation Method for Damage to Oil Reservoirs Caused by Drilling Fluids and Completion Fluids" and NB / T10030-2016 "Indoor Evaluation Method for Damage to Coalbed Methane Reservoirs Caused by Drilling Fluids and Completion Fluids".

[0069] The test results of the protection performance of drilling and completion fluid on microfractured rock reservoirs are shown in Table 2 below:

[0070] Table 2

[0071]

[0072]

[0073] As shown in Table 2, the micro-fractured reservoir protection drilling and completion fluids of the various embodiments of the present invention cause minimal damage to reservoir permeability, have a short filter cake formation time, and a high temporary plugging rate (all greater than 90%). The average acid solubility of the mud cake is greater than 80%, allowing it to be quickly dissolved and dispersed by acid during completion operations, facilitating its complete removal from the wellbore and flushing to the bottom of the well, thus clearing the gas flow channels from the reservoir to the wellbore. The average flowback recovery rate after acid washing is greater than 90%, demonstrating a significant reservoir protection effect. In Examples 4-6, compared to Example 1, the filter cake formation time is increased, while the temporary plugging rate and mud cake acid solubility are reduced. In Comparative Example 1, compared to Example 1, the different weight proportions of the drilling and completion fluid components significantly increase the filter cake formation time, significantly reduce the temporary plugging rate and mud cake acid solubility, and severely decrease the reservoir protection effect. In Comparative Example 2, compared to Example 1, the different weight proportions of the filtration loss reducer, viscosifier, and plugging agent significantly increase the filter cake formation time, significantly reduce the temporary plugging rate and mud cake acid solubility, and severely decrease the reservoir protection effect.

[0074] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A drilling and completion fluid, characterized in that, The drilling completion fluid comprises the following components in parts by weight: a fluid loss additive 1.5-2 parts, a viscosity increasing agent 0.3-0.5 parts, an inhibitor 0.5-1.5 parts, a lubricant 1.5-2 parts, an anti-water lock agent 0.5-1.5 parts, a plugging agent 5.5-8.8 parts, and water 100 parts; The fluid loss additive is at least one selected from carboxymethyl cellulose, modified starch, humic acid, resin fluid loss additive, and acrylamide polymer. The viscosity increasing agent is at least one selected from xanthan gum, modified guar gum, modified cellulose, and acrylamide polymer. The plugging agent is nano polymer, calcium carbonate, high acid soluble fiber, and ultra-low permeability treatment agent, and the weight ratio of the nano polymer, calcium carbonate, high acid soluble fiber, and ultra-low permeability treatment agent is (1-2):(2-3):(1.5-2):(1-1.5). The nano polymer is nano polyester.

2. The drilling and completion fluid of claim 1, wherein, The fluid loss additive is carboxymethyl cellulose and / or modified starch.

3. The drilling and completion fluid of claim 1, wherein, The viscosity of the carboxymethyl cellulose is 100-300 mPa·s.

4. The drilling and completion fluid of claim 1, wherein, The viscosity increasing agent is xanthan gum.

5. The drilling and completion fluid of any of claims 1-4, wherein, The inhibitor is at least one selected from polyamine, asphalt, polyalcohol, silicate, and ionic inorganic salt.

6. The drilling and completion fluid of claim 5, wherein, The inhibitor is polyamine.

7. The drilling and completion fluid of any of claims 1-4, wherein, The lubricant is at least one selected from diesel-based lubricant, mineral oil-based lubricant, vegetable oil-based lubricant, sulfonated tall oil lubricant, polyalcohol, and synthetic ester.

8. The drilling and completion fluid of claim 7, wherein, The lubricant is polyethylene glycol and / or polyglycerol.

9. The drilling and completion fluid of claim 8, wherein, The lubricant is polyethylene glycol.

10. The drilling and completion fluid of any of claims 1-4, wherein, The anti-water lock agent is at least one selected from low-carbon monohydric alcohol, alcohol ether, non-ionic surfactant, and fluorocarbon surfactant.

11. The drilling and completion fluid of any of claims 1-4, wherein, The calcium carbonate is ultra-fine calcium carbonate with an average particle size of 1250-2500 mesh.

12. The drilling and completion fluid of any of claims 1-4, wherein, The high acid soluble fiber has a length of 20-50 μm and a diameter of 0.5-3 μm.

13. The drilling and completion fluid of any of claims 1-4, wherein, The ultra-low permeability treatment agent has an average particle size of 50-1500 mesh.

14. The drilling and completion fluid of any of claims 1-4, wherein, The drilling completion fluid has a density of 1.02-1.08 g / cm 3 .

15. The drilling and completion fluid of any of claims 1-4, wherein, The drilling completion fluid has an apparent viscosity of 22.5-28.5 mPa·s and a plastic viscosity of 16-20.5 mPa·s.

16. The drilling and completion fluid of any of claims 1-4, wherein, The drilling completion fluid has a dynamic shear force of 6.5-8 Pa and a static shear force of (2-2.5) / (4.5-6) Pa / Pa.

17. Use of the drilling completion fluid according to any one of claims 1-16 in protection of micro-fracture reservoirs in tight gas reservoirs.

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